The harvesting of agricultural crops typically involves the use of large farm implements that are commonly known as combines. Combines are used to cut, thresh, and clean various types of grain. Combines are large and expensive machines that are often used in one field and then moved to other fields for work there. Because combines are extremely heavy and wide, the trailers that carry them between fields must be wide and heavy structures in order to be able to handle the size and weight of the combine.
While it is desirable for efficiency to be able to transport two combines on a single trailer, weight and size considerations make this generally impractical for modern combines. In order to be able to haul two combines at once, the trailer must be wide enough and long enough to handle the size of the combines. This, together with the structural requirements of the trailer, result in the trailer being unduly heavy. The trailer, together with two combines loaded on it, is thus too heavy to comply with highway regulations regarding weight limits. Consequently, it is common practice for combines to be carried between fields one at a time, each on its own trailer. This inefficiency adds to the cost and inconvenience involved in agricultural harvesting operations.
Other types of large equipment face similar problems. For example, bulldozers and other large earth moving and construction machinery are too large and heavy to be easily transported between job sites. Many types of vehicles, both track driven machines and wheeled machines, are subject to the same transportation difficulties.